A coordinate measurement machine is used to map or measure the shape and dimensions of an article. For this purpose, the machine includes a measuring envelope or chamber within which the article to be measured is positioned, such as upon a suitable support or base. A probe is moved within the measuring envelope to contact either preselected points or randomly selected points upon the article. The movements of the probe are recorded and may be translated into three dimensional readings, as for example, into X, Y and Z axis readings, or into other useful data. Thus, when the probe contacts a point on the surface of the article, a signal is produced which is converted into coordinate measurements or other data through a suitably programmed computer.
The measurements produced by the coordinate measuring machine probe contacts with the article may be used for a variety of purposes, including producing drawings of the article, determining surface shapes or contours, assisting in designing the article, determining dimensions and volumes, etc. The sizes and construction of coordinate measurement machines may vary, but typically they are of a substantial size in order to measure substantial size items. For example, a coordinate measurement machine may be used to measure an automotive engine block, or it may be used to measure an automobile body or similarly large articles.
Because accurate measurements are usually required, the accuracy of the coordinate measuring machine itself must be periodically tested. For that purpose, a suitable gauge is needed for producing test data generated by test movements and contacts of the probe. That test data can be used to determine equipment inaccuracies and needed compensations for any such inaccuracies.
The probe in a coordinate measurement machine is typically mounted upon an arm connected to a movable support system by which the probe may be moved three dimensionally within the envelope or chamber or volumetric area within which the measuring is performed. Thus, inaccuracies may arise because of varying tolerances or dimensional inaccuracies of the parts of the probe support system. Such inaccuracies may vary at different places or probe positions within the envelope. Thus, it is desirable to provide a gauge system which can be used to determine the accuracy of the probe generated measurements between spaced apart points located at numerous places within the envelope. This is particularly needed because the amount of measurement inaccuracies may change materially at the outer areas of the measuring envelope as compared wih central locations of the envelope due to greater movements of the probe support system at the outer areas.
In the past, testing the accuracy of the measurements produced by a coordinate measurement machine has been relatively time-consuming. When the coordinate measurements are tested, the equipment is unavailable for its measuring function which, because of the expense of such equipment, is costly down-time. Thus, there has been a need for a gauge system which is usable to rapidly check the accuracy of the measurements of a coordinate measuring machine within all of the portions of the measuring envelope. This invention relates to a ball bar gauge system useful to produce measuring data for testing the accuracy of a coordinate measurement machine.